Coating and coloring metals



Patented Mar. 31, 1931 PATENT OFFICE ALADAR PACZ, OF CLEVELAND, OHIOCOATING AND COLORING METALS N0 Drawing.

This invention relates to the coating of metals either for reservativeor decorative purposes and has or its object the provision of a simple,convenient and inexpensive process whereby certain common metals, andmore particularly those subject to tarnish and corrosion, can beprovided with a thin, adherent, coating which is pern'ianent .andnon-corrodible under all ordinary conditions, which is artisticallycolored and of pleasing appearance, and which constitutes a satisfactoryand enduring foundation for paint, enamel and other coatings; theprovision of a process which does not require electric potential, eitherexternal or internal whereby coatings of different colors can becontrollably produced; while further objects and advantages of theinvention will become apparent as the description proceeds.

The invention is based upon the peculiar properties of certainmolybdenum compounds and consists essentially in depositing upon thesurface of the article to be coated or colorcd an adherent coating ofsubstantial density and hardness, consisting apparently of one or moreof the lower oxides of molybdenum formed thereon in situ. The formationof this coating oi'l'ers varying degrees of dilficulty depending to someextent upon the nature of the metal, but even more upon the contents ofthe bath, since the addition of certain chemical ingredients appears toactivate or intensify the action, increases the density and adherence ofthe coating, and in conjunction with the time and temperature, controlsthe color. This action can also be intensified, and extended to ordinarynonactive metals b the imposition of an electrical potential ut it is animportant feature of my invention that the common metals, iron, steel,tin, aluminum, zinc, cadmium, lead, and even magnesium, can be coatedsuccessfully without the employment of potential.

In the performance of my said invention I preferably employ a solutionof one of the water-soluble molybdenum compounds such as the molybdateof one of the alkali metals, potassium, sodium, lithium or ammonium, theparticular compound which I prefer being rapid.

Application filed March 23, 1925. serial No. 17,799.

, aqueous solution of a very great range of concentration since asolution containing less than one-tenth of one percent of this compoundis entirely operative, though slow, and a solution containing upwards oftwo percent of the same is likewise operative though more The onlydraw-back is that with undue concentrations (say upwards of 10%) acoating is obtained which is not so dense or closely adherent although Ido not limit myself in this respect since there may be some caseswherein these qualities may be less im-. portant than speed. To thissolution I preferably add a suitableactivating reagent such as a solubleoxalate, or electrol te such as the sulphate, chloride, etc., preferablyof the same base i. e. ammonium, but on occasion even the pure aciditself. The proportion of this ingredient can be varied considerablyaccording to the metal, the temperature, the time of treatment, and thenature and color of the coating desired. A coating of some kind canalways be obtained within the limits of operation herein described, andsuch coating can be made darker in color by increase of molybdenumconcentration or elevation of temperature or longer immersion oraddition of such activating reagent (or electrical potential).

Articles made of or coated with iron, steel,

tin, lead, aluminum, zinc, cadmium, or even magnesium, when carefullycleaned and im mersed in such a solution become coated with a denseadherent protective coating generally of a gloss and shiny character (ascompared with the 1111 black of most rust proofing processes) andexhibiting coloration of all kinds depending upon the concentration andtemperature and composition of the liquid and the duration of treatment.These colors range through all gradations through yellow, red, green,and brown to black. It is not al: ways possible to obtain the darkercolors in the cold and in general it ma be said that the higher thetemperature an the greater the concentration the easier it is to obtainthe darker shades. The colors depend almost entirely upon thecomposition and temperature of the solution and the duration of contactand only to a small degree upon the color of theoriginal metal; thecolors are generally iridescent but very permanent. Alloys behave likethe metal which predominates in their composition; thus zinc alloys,such as those employed in die casting, can be treated very successfullyin this manner. A slight acidity is geuerall desirable.

The activity o the solution can be an meuted by the addition of certainother su stances. One class of substance having this effect is that ofelectrolytes, for examplethe water-soluble chlorides, nitratessulphates, etc. These salts may possess any desired base, although Iprefer those on alkali bases, and I particularly recommend the use ofthe same base as already present in the solution e. g. ammonium chloridewhen ammonium molybdate is being used. Another class .of sub stancesexhibiting this energizing effect on the solution is found in theorganic acids such as gallic acid, tannic acid, oxalic acid, or'theirsalts. The proportion of the energizing ingredient can be varied verywidely and same may be present in either greater or less proportion thanthe molybdenum compound. Articles ofzinc, iron, lead and their alloyswhen immersed in this activated solution can be coated noticeably morequickl than in the plain solution first described, an in addition acoating can be obtained with convenient speed on certain other metalssuch as aluminum, copper, nickel, tin, and their alloys which exhibittoo slow a reaction in the plain solution. The speed of reaction can beincreased by heating, although the efl'ect even of this solution onnickel and tin is rather unduly slow. I

In order further to expedite the reaction and to extend it to othermetals, thus facilitating the coating of nickel and tin and enablingcoating of gold, silver, latinum, tungsten, chromium and the likeIimpress upon the article a slight negative E. M. F.;. this may be doneeither by immersing it in contact with a sheet of electropo'sitive metalcontained in the same bath (such as zinc or magnesium) or by attachingthe article to the negative pole of a battery, the positive pole ofwhich is attached to a conducting plate of some kind suspended incontact with the liquid. In the former case, I obtain the best resultsby arranging the articles and contact plates successively, an article tobe coated being located between and in contact with two'zinc plates (forexample). In case an exterior battery be employed as a source of E. M.F., its volume of current seems to have little or no eifect. A commondry battery is suflicient to operate a large size tank, while a commonstorage battery can be employed for an indefinite time withoutappreciable loss of charge. Thecomposition of the contact plate to whichthe positive pole of the battery is connected also appears not to beimportant. I generally make it of zinc since this substance is cheap,readily available and a good conductor; a hough it can equally well bemade of carbon, iron lead, or other metals, provided only that it be ofsome substance which does not dissolve with the roduction of ingredientswhich poison the ath such substances as zinc, iron, cadmium andmagnesium which tend to evolve hydrogen .from acid or aqueous solutions;owing to secondary reactions this deposit would ordinarily be in theform of molybdic acid but the nascent hydrogen so far neutralizes thattendency as to give rise to a series of lower oxides which adhereclosely to the surface of the article with the decorative and protectiveeflects above described, Indeed it is possible that some of the coatingconsists of metallic molybdenum though this is doubtful.

By the process above described it is possible to color nearly everymetal (excepting those like sodium and lithium which decompose water)for example gold, silver, platinum, tungsten, chromium, copper, zinc,nickel, tin, lead, magnesium, aluminum and their alloys. Furthermorethese coatings are permanent, untarnishable, ornamental and Veryartistic. The color is iridescent and proof against handling, washing,rubbing etc. although it can be scraped away by abrasives or by hardtools. Aricles of iron and steel treated in this manner exhibit anincreased resistance to weather and corrosive conditions; even a stickof magnesium is notably protected from salt water by this treatment. Thecoating thus produced also serves as a very satisfactory foundation forpaint, enamel and the like by which the article is still furtherprotected against corrosive influence, this being the preferredprocedure in large scale treatment of iron and steel, as

for example in connection with automobile bodies.

I do not limit myself to the use of such molybdenum compounds as aregenerally considered readily soluble, of which the molybdates are anexample, inasmuch as I find it possible to operate successfully withbaths containing excess amounts of other molybdenum compounds such asmolybdic acid in intimate contact therewith as by being suspendedtherein. The small amount of this compound which goes into solutionunder such conditions serves to produce the result in question eventhough its percentage in solution is very small. Also I do not limitmyself to temperatures, nor to the duration of treatment, since one tothree minutes immersion is generally sufiEicient in the case of areadily reactive solution while an increased time of immersion isdesirable with the more attenuated solutions. This time element alsodepends upon the temperature and upon the color desired.

My improved process is useful both artistically and technically,artistically in enabling the production of pleasing and permanent colorson fittings, fixtures, and art objects made of inexpensive metals (suchas electrical fixtures, biulders hardware,interior decorations, plates,placques, statuary, bricabrac, etc.) or technically in rust proofingiron and steel, coating tin cans and other food containers, andproducing a foundation to which paint and Varnish will adhere morefirmly than to the metal itself. Accordingly I do not limit myself inany respect except as specifically recited in my several claims.

Having thus described my invention what I claim is:

1. The process of coating articles consisting at least superficially ofiron, steel, tin, aluminum, zinc, cadmium, lead, or magnesiuni whichcontains the step of simple immersion in a solution containing a solublemolybdate and a soluble oxalate.

2. A dipping solution for the purpose described containing a solublemolybdate and a soluble oxalate.

3. The process of coating metal articles which contains the step ofimmersion in circuit with a zinc anode in a dilute aqueous solution ofammonium molybdate, together with a larger qantity of secondnon-alkaline ammonium compound.

4. The process of coating metal articles which contains the step ofimmersion in electric circuit with a zinc anode in aqueous solution of asoluble molybdate, and a second non-alkaline salt which constitutes anelectrolyte.

In testimony whereof I hereunto aflix my signature.

ALADAR PACZ.

